The present invention relates to a wiring board and a method of making the same, and more specifically, to a wiring board having stacked embedded capacitors and a method of making the same.
Low inductance capacitance in the range of microfarads is required for decoupling of microprocessor cores. There are a number of approaches for providing such capacitance, including incorporation of capacitance within the microprocessor, such as deep trench on-board capacitors, MIMcap, and interposer technologies, as well as incorporation of the capacitance onto the microprocessor wiring board, including surface mount capacitors, backside capacitors and embedded capacitors. While all of the above-mentioned approaches have been useful, they have limitations that may make them undesirable for use with advanced microprocessors having a relatively large number of cores, such as 16 to 24 cores. For example, the use of approaches that place the capacitance on the microprocessor are limited due to the circuit density associated with the large number of cores.
In this regard, the use of wiring boards with embedded capacitors is desirable to place the capacitors as close as possible to the microprocessor, including under or in the shadow of the microprocessor. However, wiring boards with current single-layer embedded capacitors are not capable of providing enough capacitors under the microprocessor. While wiring boards with stacked embedded capacitors have been proposed, the internal wiring architecture associated with these board designs does not provide sufficient interconnection capability and/or flexibility to allow the stacked capacitors to be accessed individually. For example, a wiring board with stack embedded capacitors is disclosed in US Patent Publication No. 2013/010594381A1. In this disclosure, the innermost electrodes of the stacked capacitors are electrically connected to one another. The innermost electrodes are not independently accessible which limits the flexibility of wiring board and microprocessor designers when using the stacked embedded capacitors in various circuit designs, particularly the ability to use the stacked embedded capacitors to provide needed decoupling capacitance in microprocessor circuit designs with large numbers of microprocessor cores.
Therefore, it is very desirable to develop stacked embedded capacitor designs that provide improved access to the capacitor electrodes and improved circuit design flexibility, including the ability to increase access to individual stacked embedded capacitors, particularly for use with microprocessors with a large size or footprint and relatively large numbers of cores, and more particularly where the capacitors may be embedded in the wiring board under the microprocessor.